This invention concerns a novel process for treating polyfluorocarbon-coated razor blade cutting edges, particularly polytetrafluoroethylene-coated razor blade cutting edges.
Uncoated razor blades, despite their sharpness, cannot be employed for shaving a dry beard without excessive discomfort and pain, and it is as a practical matter necessary to employ with them a beard-softening agent such as water and/or a shaving cream or soap. The pain and irritation produced by shaving with uncoated blades are due to the excessive force required to draw the cutting edge of the blade through the unsoftened beard hairs, which force is transmitted to the nerves in the skin adjacent the hair follicles from which the beard hairs extend, and, as is well known, the irritation produced by excessive pulling of these hairs may continue for a considerable period of time after the pulling has ceased. Blade coatings were developed to solve these shortcomings.
Granahan et al., U.S. Pat. No. 2,937,976, issued May 24, 1960, describes a "coated" blade which provides a reduction in the force required to cut beard hair. The coating material consists of an organosilicon-containing polymer which is partially cured to a gel which remains adherent to the blade. Although these coated blades met with considerable commercial success, the coatings were not permanent and would wear off relatively quickly.
Fischbein, U.S. Pat. No. 3,071,856, issued Jan. 8, 1963, describes fluorocarbon-coated blades, particularly polytetrafluoroethylene-coated blades. The blades may be coated by (1) placing the blade edge in close proximity to a supply of the fluorocarbon and subsequently heating the blade, (2) spraying blade with a fluorocarbon dispersion, (3) dipping the blade into a fluorocarbon dispersion or (4) by use of electrophoresis. The resulting blade was later heated to sinter the polytetrafluoroethylene onto the blade edge. Fischbein is silent on the use of fluorocarbon solutions.
Fischbein, U.S. Pat. No. 3,518,110, issued Jun. 30, 1970, discloses an improved solid fluorocarbon telomer for use in coating safety razor blades. The solid fluorocarbon polymer has a melting point between 310.degree. C. and 332.degree. C. and has a melt flow rate of from 0.005 to 600 grams per ten minutes at 350.degree. C. The molecular weight is estimated to be between 25,000 and 500,000. For best results, the solid fluorocarbon polymer is broken down to 0.1 to 1 micron particles. The dispersion is electrostatically sprayed onto stainless steel blades.
Fish et al, U.S. Pat. No. 3,658,742, issued Apr. 25, 1972, discloses an aqueous polytetrafluoroethylene (PTFE) dispersion containing Triton X-100 brand wetting agent which is electrostatically sprayed on blade edges. The aqueous dispersion is prepared by exchanging the Freon solvent in Vydax brand PTFE dispersion (PTFE+Freon solvent), distributed by E.I. DuPont, Wilmington, Del., with isopropyl alcohol and then exchanging the isopropyl alcohol with water.
Trankiem, U.S. Pat. No. 5,263,256, issued Nov. 23, 1993 (Docket No. 7951) discloses on an improved method of forming a polyfluorocarbon coating on a razor blade cutting edge comprising the steps of subjecting a fluorocarbon polymer having a molecular weight of at least about 1,000,000 to ionizing radiation to reduce the average molecular weight to from about 700 to about 700,000; dispersing the irradiated fluorocarbon polymer in an aqueous solution; coating said razor blade cutting edge with the dispersion; and heating the coating obtained to melt, partially melt or sinter the fluorocarbon polymer.
Trankiem, U.S. patent appn. Ser. No. 08/232,197, filed Apr. 28, 1994 (Docket No. 4210) discloses a method of forming a polyfluorocarbon coating on a razor blade cutting edge which comprises subjecting a fluorocarbon polymer having a molecular weight of at least 1,000,000 in dry powder form to ionizing irradiation to reduce the molecular weight of the polymer, forming a dispersion of the irradiated polymer in a volatile organic liquid, spraying the dispersion on to a razor blade cutting edge and heating the coating obtained to sinter the polyfluorocarbon. The polyfluorocarbon preferably is polytetrafluoroethylene and irradiation preferably is effected to obtain a telomer having a molecular weight of about 25,000.
U.S. Pat. No. 5,328,946 to Tuminello et al. discloses perfluorinated cycloalkane solvents for dissolving high melting polymers containing tetrafluoroethylene. These solvents are said to dissolve such polymers more rapidly, and/or are more stable, than previously known solvents. Also disclosed is a process for dissolution of the polymers and their resulting solutions. The solutions are useful for making polymer films, coatings and for encapsulating objects.
U.S. Pat. No. 5,364,929 to Dee et al. discloses a process for dissolving high melting polymers containing tetrafluoroethylene units at pressures greater than autogenous pressure, using selected halogenated solvents that are often not solvents resulting from this process. The resulting solutions are said to be useful for preparing fibers and paper-like webs from these polymers.
U.S. Pat. No. 4,360,388 discloses certain solvents for tetrafluoroethylene (TFE) polymers, including perfluorodecalin, perfluoromethyldecalin, perfluoromethyldecalin, perfluoromethylcyclohexane and perfluoro(1,3-dimethylcyclohexane). All of these solvents are believed to have critical temperatures below 340.degree. C., and hence are not solvents for PTFE.
B. Chu, et al., in a series of papers [Macromol., vol. 20, p. 702-703 (1987); Macromol., vol. 21, p. 397-402 (1988); Macromol., vol. 22, p.831-837 (1989); J. Appl. Polym Sci., Appl. Polym. Sym., vol. 45, p. 243-260 (1990)] describe the measurement of the molecular weight of polytetrafluoroethylene (hereinafter sometimes PTFE) in solution. The solvents used in these studies were perfluorotetracosane and oligomers of poly(chlorotrifluoroethylene).
P. Smith and K. Gardner, Macromol., vol. 18, p. 1222-1228 (1985) review and discuss both the practical and theoretical aspects of dissolving PTFE. As reported by them, PTFE has been dissolved only in perfluorokerosenes and perfluorinated oils, in other words, perfluorinated higher molecular weight alkanes. They report that PTFE will not dissolve in perfluorodecalin, octafluoronaphthalene or decafluorobenzophenone.
U.S. Pat. No. 3,461,129 reports in Example A that 4-ethoxy-2,2,5,5-tetrakis(trifluormethyl)-3-oxazoline dissolves low-melting (83.degree.-145.degree. C. melting point) PTFE. There is no mention of dissolution of higher melting PTFE.
Polytetrafluoroethylene coatings on razor blade cutting edges are clearly known in the art. Furthermore, it appears that various solvents systems have been proposed in the literature for polytetrafluoroethylene. However, the art fails to appreciate the importance of a thin PTFE coating; especially during the initial, first shave. Furthermore, the art is silent on selective removal of polytetrafluoroethylene from razor blade cutting edges.
It is an object of the present invention to provide a razor blade cutting edge with a thin, well adhered coating which provides significantly improved initial cutting force effects when compared with the prior art. This improvement in cutting force translates to an improved first shave and often translates to improved subsequent shaves.
It is also an object of the present invention to provide a razor blade which causes fewer nicks, improved comfort, and/or improved closeness.
Furthermore, it is an object of the present invention to provide a method for producing these improved blades. The process utilizes novel processing steps.
These and other objects will become evident from the following.